


The Secret Avenger: Civil War

by eatyourhartout



Series: The Secret Avenger [3]
Category: Percy Jackson and the Olympians & Related Fandoms - All Media Types, Percy Jackson and the Olympians - Rick Riordan, The Avengers (Marvel Movies), The Avengers (Marvel) - All Media Types
Genre: Alternate Timelines, Alternate Universe - Canon Divergence, Avengers - Freeform, Civil War (Marvel), Crossover, Demigods, Fix-It of Sorts, Gen, Hydra (Marvel), Light Angst, Pre-Avengers: Age of Ultron (Movie), Wings, canon pairings - Freeform, maximoff twins
Language: English
Status: Completed
Published: 2018-12-23
Updated: 2018-12-23
Packaged: 2019-09-25 10:21:02
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 5
Words: 4,584
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17119529
Author URL: https://archiveofourown.org/users/eatyourhartout/pseuds/eatyourhartout
Summary: They might have won during the events of the Triskelion, but HYDRA is still a threat.While fighting the rogue terrorist group, Tony makes a discovery that could tear the team apart.OC Demigod, set before Age of UltronPost Giant's War; Post Olympus's SoldierMinor Swearing





	1. Chapter 1

“I don’t care. He killed my mom.”

The cold accusation rang across the room. The three men were frozen in a horrible tableau. Steve stood defensively in front of Bucky, bruises on his face already healing. Tony’s hand hovered over the gauntlet on his wrist, having begun to summon his suit. All three of them were panting slightly, the sound of heavy breaths filling the room. In the next moment Tony lunged forward, his blaster firing, while Steve rolled over the broken glass of the shattered table, shield in position to deflect the blast. Bucky leapt over him, arm slamming into Tony. The billionaire fell back, but to his _human_ credit, recovered quickly, punching the former assassin with his gauntleted arm. Bucky punched back, slamming Tony into the ground. It went on like that; Tony hardly holding his ground against the two super soldiers. 

“HEY!” They all froze. Fist raised, blaster glowing, shield prepared to slam down. Sy stood in the door way, eyes wide in horror. 

“What in _Hades_ is going on in here?” The nineteen year old demigod’s expression was thunderous. Large wings trailed behind her, burned and damaged patches still apparent even nine months after the injury, a guitar tucked under one arm. She stepped into the room surveying the destruction. They were in one of SHIELD’s many safehouses; somewhere deep in Eastern Europe. The Avengers had reformed in order to take down HYDRA. They’d been waging war on the terrorist organization ever since the uprising in DC in January, and had just successfully completed another mission. The secret Avenger’s eyes widened as she spotted the miraculously undamaged tablet on the floor. She slowly bent down and picked it up, her eyes tracking the events on the screen.

The tablet had continued to play the video on loop, even after it had been dropped to the floor. Snow fell gently across the screen, peaceful, as bright headlights flashed in the distance. Her eyes were glued to the screen, even as the men looked away. They didn’t need to look at it anymore to know what happened next. A car crash. The glint of a metal arm. A red star. Flashes of light as the gun fires. Dark empty eyes over a black mask as the assassin turned away from his victims.

Sy looked up from the screen, gripping the tablet so tightly her knuckled had turned white.

“What’s this?” She asked quietly. None of the men were able to respond.

“Steve?” She asked, looking first to her brother. The first avenger looked away. Sy turned to her friend next.

“Tony?” The inventor refused to meet her gaze, training both his blackened eyes instead on the tablet she clutched in one hand.

“James?” She asked softly, finally turning to the newest Avenger.

“What is this?” The winter soldier looked up at her, dark eyes haunted.

“Me.”


	2. Chapter 2

_Sy_

The room was completely silent. Sy carefully set the tablet down, guitar still firmly in hand. She wasn't about to set down her most effective method of diffusing the incredibly tense situation. This was worse than the time the Mind Stone had been forcing them to fight all those years ago. Because now, it was personal. A betrayal of the highest order had occurred. The anger was  _real_.

She wasn't sure what started it, but suddenly Steve had lunged, shield still held up defensively, and Tony reacted with his repulsors firing; James had dove behind the ruined couch for cover. The room devolved back into chaos. Repulsors firing, metal crunching, glass shattering, the flash of red and blue as Steve's shield flew through the air. Silver glinted as Buc- James threw a punch. Sy dropped the tablet, desperately lunging forward to break up the men, but then someone hit her. 

She flew back, thrown across the room by the force of the blow. Her head slammed back, bits of plaster flaking off from the wall. White hot pain shot through her and black spots danced in her eyes. The pain was so intense she couldn't even scream as her left wing bent under her body in the wrong direction. Sy turned to her side, fighting the urge to pass out from the pain.

When she finally had the strength to stand, her eyes widened. Buc-  _James's_ metal arm had been blasted clear across the room, the man on the floor clutching the ruined stump of his prosthesis. Steve stood above a downed Tony, shield raised above his head as dark anger clouded his features. She reached out, and her hand curled around the neck of the guitar, power curling around her. Sy didn't even think as she swung the instrument into her lap, as the air around her thrummed with energy. 

She strummed the first cord, shoving all her power into the first few notes. The room froze under the force of her will. Tears filled her eyes as she slowly began to play a melody. As the chords spilled from the guitar, soft lyrics fell from her lips.

_All the things you got,_

_All the things you need_

_Who bought you cigarettes,_

_Who bribed the company to come and see you, honey_

Power infused her voice, filling the music. It danced through the air, threading through her soul, ripping it to pieces as she  _made_  them listen. She could taste the magic her godly heritage had granted her, even as tears poured down her cheeks. The men slowly separated, but Sy could see their muscles straining and tense as they fought her control. She pressed harder, overpowering their anger until they were nothing but putty in her hands. Self loathing filled her as she sang and played, her wings throbbing dully on her back where she'd landed awkwardly. She invaded their minds; hunting through their emotions to make them calm, tapped into pools of patience, dragged into the deep reservoirs of love they carried inside. 

She built steel cages for the anger and hurt that filled the room, and using her music kicked and shoved it away. Pushed away the vengeance that filled Tony and the self-righteous anger that had overcome Steve. She soothed the fear and guilt that James was feeling. She had no idea how long she'd be able to force them to have level heads, but she hoped it would be long enough. Her energy was draining away quickly, partly because she had yet to regain her full strength after she'd been injured in DC and partly because she'd always refused to exercise her gifts in this manner before. But now she had no choice. If she didn't intervene, someone was going to die. And even if no one did, it would tear the team, their  _family_ apart.

When the men were in separate corners of the room, and she could feel the artificial calm she'd created for them, Sy slowly stopped singing, even though she continued to play. She felt her power stretch and flow in ways she'd always known she was capable of, but had  _never_ used.

"Steve, James. Get out." She ordered in a shaky voice, even though it was still filled with power. If there was a monster within a mile of the cabin, they were going to attack. There was no way any supernatural being wouldn't feel the power she had unleashed in that room. She had a feeling Thor and Loki would already be on their way to her location to investigate the power surge.

Steve and James left stiffly, still more than halfway under her influence. But she also knew that they understood being in the same room as Tony right then was a bad idea. Heaving breaths shook her body as she tried to reign in her conflicting emotions. She looked up at the distraught Tony. She'd shoved away his anger; forcing him to confront the other half of his pain. Grief. Tony sank to the floor as sobs racked his body. Sy couldn't bring herself to comfort him, not after the way she'd just violated him mind. She stepped away from her friend, hands shaking, body growing cold as she trembled.

"I'm sorry." She whispered, before swallowing hard.

"Please ,Tony. I know seeing that video must have been horrible, that knowing what he did to them is tearing you apart right now. But  _please_ , help him. It wasn't his fault. It's not his fault." She whispered. Dark pain filled eyes lifted from the ground to meet hers.

"Please Tony. I'm so sorry." She pleaded one more time before turning and fleeing.

**Notes for the Chapter:**

> The song is Thinking About You by Radiohead


	3. Chapter 3

_ Sy _

 

It hadn’t even registered to her that she’d left the safe house until Sy had gotten more than a mile away and the full impact of what she had done slammed into her. 

_ She’d controlled their minds. _

It had always been her one rule. Free will was something she would never take. Sy had always skirted around the issue as a demigod, and eventually as an Avenger. She manipulated, influenced, even exploited people’s emotions, weaknesses and desires. But she never outright stole control from anyone. Even with the Chitauri, she’d only redirected their goal. She didn’t make them stop fighting, she'd just convinced them that the fight was someplace else. That instead of humans, the enemy was a comrade. It was still wrong, but in a different way. It was a grey area she could live with. 

She collapsed to her knees, snow soaking through her jeans. Her hands hit the ground, and her hair swung around her shoulders as her whole body heaved and she retched. As she sat up, wiping the bile away from her mouth with shaking hands, she finally noticed the cold. She’d left the cabin in such a hurry that she hadn’t bothered with a jacket. If she didn’t get someplace warm soon, she knew she risked not only getting sick, but seriously injured. Even though it was early November, it was still freezing where they were. The last of her adrenaline faded away, allowing the pain she’d repressed to return in full force. 

The side of her face throbbed from where somebody had hit her. The back of her head ached from its impact with the wall. Her left wing practically _screamed_ its displeasure at her, and she was forced to hold it at an awkward angle so it hurt her less. She could feel blood trickling through some of her secondary feathers. She’d probably reopened one of the many injuries that still hadn’t healed. 

Loki suddenly popped up in front of her. She forced herself to her feet, swaying slightly as she did. He surveyed her quickly, sharp eyes taking in the full situation quickly. Sy knew that he was reporting back to the others on the state of her condition. 

“Little godling, you are hurt.” He said simply, worry creasing his forehead. She sighed and plopped back down onto the ground. She could hear the hum of the Ironman suit, the rumble of an engine and taste ozone in the air. Even if she wanted to keep leaving, the others would catch up quickly; especially because she still couldn’t fly well. Sy had only recently returned to the skies, her rehabilitation moving incredibly slowly. 

She didn’t have to wait long before everyone showed up. The projection faded away when the _real_ norse god of mischief stepped out from the passenger seat of the jeep. Tony and Thor touched down just as the other five members of their team piled out of the car. 

“Reindeer Games, is this hers?” Tony had stepped closer to her, his faceplate raised to reveal a black eye and several small cuts on his face. Loki nodded shortly, even though the god’s eyes remained trained on her. The billionaire let out a sharp breath through his nose. He looked back over his shoulder, deliberately avoiding looking at either Steve or James. Sy flinched when she noticed the slightly stiff way all three men walked, as though they didn't have full control over their own limbs. 

“Bruce, she’s been vomiting blood. She took a hard hit from somebody back at the cabin. We need to get her to medical.” Sy ignored the comment as she locked eyes with the one person she had grown to trust most in all the world.   

“Steve, how could you?” She whispered. Pain clawed at her heart, and guilt ate at her gut. She was desperate for anything to relieve the horrible feelings that were bottled up inside of her; and Steve, brave, good, kind Steve. Her brother, had unleashed apart of him that she  _ knew _ he was afraid of. A part of him he told her he kept locked away as deeply as he could because it scared him. And he had unleashed it; she’d seen it when she’d locked it away. When she had forced all three men to bend to her will, crossing her only true boundary to protect them all. 

“He’s my friend.” Came the quiet answer, shame flushed along his cheeks. She didn’t know who he was referring too; not telling Tony about his parents to protect him from reopening old wounds, or nearly killing a teammate in order protect James. Or maybe he was talking about Howard Stark. She couldn't be sure because they were all his friend. 

“Do you have any idea how terrifying that was to walk into?” She whispered hoarsely, suddenly unable to breath. Steve shook his head slightly, his gaze still locked on hers.

“And then you didn’t stop. And then I, I had too…” She trailed off, her chest heaving as she shook silently. Steve took a single step forward and she flinched away violently. She collapsed to the ground, sobbing violently. Tony and Bruce both dropped to the ground next to her, both geniuses checking her over. Rather Bruce was, since Tony was laser focused on the exchange between her and Steve. 

“ _ Sy _ .” He breathed out. Tears had gathered in his eyes too. Sudden understanding had lit into him, and guilt clouded his features. 

“Sy, I never meant for-” 

“But it did.” Tony broke in. She looked up through teary eyes to see her friend’s hard glare levelled on Steve. 

“Tony, you have to understand-” Steve tried, but Tony plowed right over him, stepping out in front of Sy. 

“You should have told me. _Before_ you brought him into _my_ home. Onto _our_ team. I know he wasn’t in control; just like Clint wasn't, like Loki wasn't. But  _ you should have told me. _ Whatever Jedi mind trick Sy pulled, it’s not going to last forever; so you and Barnes need to stay the _hell_ away from me for awhile.” Sy flinched when Tony said that she still had control over them. Her power had only grown over the years; but she’d always been careful to make sure that her music wore off right away. That the emotions people were left with after she played for them was their own. Steve opened his mouth, eyes tight with worry but James rested a hand over his shoulder, pulling the first Avenger back. 

“We’ll go Tony.” He said shortly, his face a mask. The clink of metal on metal alerted her that Tony had closed the faceplate. 

Two sets of hands helped to her feet, and when she looked up it was Bruce and Clint. She managed to stand shakily on her own feet when a bone chilling growl emerged from behind them. The team turned around as one, Sy flaring her wings out aggressively, even as the stretch burned painfully in her still weak and damaged muscles. Instinct and adrenaline roared through her, and strength poured back into her numb body.

Bright red eyes glowed from beneath the shadows of the trees. The massive hellhound stalked out from the forest, each step shaking the ground slightly. It was easily the size of a garbage truck, with none of the playful friendliness that Percy Jackson’s pet hellhound Mrs. O’Leary always exhibited. 

Sy reached down and tapped the holster on her side. Her sword was back at the cabin; but she’s been a demigod all her life and knew better than to be anywhere unarmed. A celestial bronze knife was strapped to her hip, and a second one down her boot. Neither one particularly sufficient to fight the gigantic monster in front of her, but more than enough to distract it long enough for the others to get away. She knew Thor and Loki couldn’t interfere; there were limits to how much even the Aesir could bend the ancient laws and none of the others could fight a hellhound.

“What the _hell_ is that?” Tony muttered. She slowly slid the celestial bronze knife out of its sheath. She raised it defensively, never taking her eyes off the monster. She ignored the echoes of a dying scream that sounded in the back of her mind. 

“Remember when I told you guys about being a demigod? What our lives are like? Well, _that’s_ a hellhound.” She moved slowly, edging out in front of her friends.

“You guys are mortal, it should leave you alone. When I tell you too;  _ run. _ ” She didn’t give them a chance to protest. She lunged forward with a yell, driving the point of her first knife into the monster’s shoulder. Yanking the second one out of its sheath, she rolled under the monster's stomach. She rammed the second knife into its’ belly, doing her best to gut the hound. As she came out from her roll, she glanced at the shellshocked Avengers. She didn’t have any time to waste. She started to sprint away into the forest, the hound chasing after her. As she ran the growls and snarls of the hellhound behind her followed closely. She knew that if she hadn’t injured it first, that the monster would have already killed her. But she was injured too, and an injured demigod was nothing more than monster bait. Better her than the Avengers though. 

Sy looked back one last time. She screamed back one last order before pelting away from her friends. 

“ _ Run! _ _”_  


	4. Chapter 4

_Steve_

_"Run!"_

It took a few seconds for the team to understand what happened. IN that moment of hesitation, Sy had already sprinted into the woods, wings streaming out behind her as the  _thing_ followed behind her, trailing gold sand like any normal creature would trail blood.

A _hellhound._

Sy had told him about them once. It had been while she'd still been living with him in his little apartment in Washington DC, before everything had gone to hell with SHIELD. He'd been woken up by her screams, and had run into the other room, shield in hand expecting an attacker. Instead he'd found Sy on the floor, tangled up in her sheets, wings flared out defensively and tears streaming down her face, breathless with sobs.

He'd managed to calm her down, and they'd talked about her nightmare. The first of many late night conversations about both of their pasts. The first night, Sy had tipped her head back, and told him the story of a quest gone wrong right after the Titan War had fully broken out. She had stared blankly at the opposite wall, her normally lyrical voice completely flat and devoid of emotion.

She'd dreamed of a mission she'd gone on. It had been three weeks after the first battle; the Battle of the Labyrinth. Her and a friend had gone on a simple scouting mission. Her friend had been inexperienced, a new camper. But it was supposed to be simple, just a little reconnaissance, and the two of them were some of the few uninjured demigods. They were so short handed, that despite everyone's reservations, they'd allowed them both to go. Only their simple mission got a lot less simple when a pack of hellhounds caught up to them before they'd gotten within twenty miles of the Titan Army. Her friend died a horrible death, and she hadn't escaped unscathed either. Sy had showed him a set of claw marks over her shoulder, the skin thick and twisted where it had scarred. She still doesn't like large black dogs because of it.

And now one was chasing after her. While she was injured and upset.  _Because of him_.

Sy had warned them all about her demigod aura, how it sometimes attracted monsters; warning them that when she used her powers excessively that the scent she gave off strengthened. She'd slip off all the time when they got together, returning to the team a little battered and bruised, shedding gold sand. Sy frequently ducked away from them after her concerts to take care of monster problems as quietly as she could before rejoining them for what ever extravagant celebration Tony liked to throw for her.

Power like hers was a supernatural homing beacon, and he knew she had used a lot when she'd controlled the room back at the cabin. Even  _he_  could feel the power Sy had been giving off, and he was mortal.

God, how could he have been so  _blind?_ He should have told Tony about his parents ages ago; but it was always hard for him to talk to Tony about his dad. Both men had been his friend, although if he could Steve would love to punch Howard for how badly he'd screwed up with Tony growing up. Doing the  _exact_  thing Howard had once privately sworn to him he'd never be.

But between the search for Bucky, and his conflicted feeling about wanting to protect Tony he'd never gotten around to it. And then, Tony found the video himself. And the mystery of  _who_ killed Howard and Maria Stark was solved. From there everything had gone to hell. He and Bucky and Tony started fighting and  _he just couldn't stop_.

It was a horrible excuse but, in the safe house, something inside him had  _clicked_  and rage like he'd never felt before had surged forward. Steve wasn't sure what he'd been angry about; Bucky for being the Winter Soldier, Tony for not understanding that Bucky had been brainwashed or himself for not having prevented the problem in the first place. Which he could have, if he'd talked to Tony the way Sy told him too months ago. But either way, he'd gone over board; the rage he felt taking over and nearly destroying the one thing in this new world he found himself living in that kept him afloat. The Avengers, the team, grounded him. And he would have thrown it all away in that moment of blind rage if it wasn't for Sy.

Sy who had broken her only rule to protect him from himself. Sy who was being chased down by a monster that stalks her dreams, still trying to protect him while they were frozen in the snow in the middle of nowhere. Sy, his surrogate sister, and legal ward, sprinted away into the woods; leading a monster away from them.  _His_   _kid_. Which she still was. Nineteen might be old for a demigod, but in the regular world, she was still a kid. And she was protecting  _them_. Not the other way around.

He didn't need to look at the rest of his team before they all surged forward, determined to follow, to help her, to  _protect_  her, when a green barrier shimmered into existence in front of them. Steve slammed into it, electricity arcing through him before he turned around angrily. The Trickster stood behind them, one hand raised in front of him, raising the barrier. Even though his eyes were hard, his hand was trembling slightly. Thor stood just behind him, muscles tense and strained, but he was frozen too. Steve made a quick check; green eyes, not blue. Not possessed.

"Bring. It. Down." Steve ordered through gritted teeth. Loki shook his head.

"You cannot help her. And we cannot interfere." The god said coldly, even though there was suspicious shimmer in his eyes. Something in the back of his mind said that the god liked not helping Sy about as much as he did; but a much darker part of him was screaming at him to  _attack_  Loki _._  To hit and punch and  _kill_ until the barrier preventing from helping Sy came down. The same part of him that had surged forward when Bucky had been in danger.

"Why not?" Tony snarled, moving to stand shoulder to shoulder with Steve. No matter their differences, Sy was more important.

"She's protecting you mortals from a monster you cannot kill, cannot even harm. But mark my words, if you tried, the hell beast would most certainly kill you." Loki said.

"And we cannot interfere. It goes against the Ancient Laws. Loki and I already subvert them in order to be a part of the Avengers. We give up much of our power and influence to help defend Midgard as we do, but in return we must respect the Divine Laws. And we are forbidden from getting involved in demigod affairs of another pantheon. Especially without sufficient tribute during battle." Thor added gravely.

"So you're saying we  _can't_ help her?" Steve snarled.

"Aye." Thor said shortly, even as he practically vibrated with repressed energy.

An anguished howl emerged from the trees, and both gods visibly relaxed. The green barrier vanished.

"She was victorious." Loki murmured with a sigh of relief. Steve felt something inside him unwind slightly at those words. Then they heard the gunfire and a short scream.

As one the team surged forward in the direction of Sy's desperate scream.


	5. Chapter 5

_ HYDRA _

 

It was a lucky coincidence. The perfect windfall. 

They sent several teams to retaliate against SHIELD and the Avengers for the most most recent raid against them, when they came across the youngest member. The secret one. 

Syrinx Melos. 

Even when they had been hidden within SHIELD, HYDRA had never been able to get much information on her. There was nearly nothing on her in public record, and even when the girl had worked for the organization, she’d been directly handled by Nick Fury; her files so classified that only he held access. Not even the defense minister had been able to access her files. No photos, no videos no after action reports on her gifts and abilities. 

But to come across her as they had; alone, injured,  _ vulnerable _ . It was almost as though the tides had turned in their favor once more. While they lost access to the scepter not even two weeks after the invasion in New York, they had enough material, enough power stored away to continue for years. Now they were close; the twins nearly ready. But they had run out resources, their research incomplete. Then the got the girl. The girl and her wings and her power.  Her power  _ sang. _ The same way the scepter’s power had. 

It had taken a fierce fight, and more than eighty percent loss for their side. The Avengers fought hard to protect her, to prevent them from taking her. But their men had come away with the prize. A prize who was now strapped down to a table; wings spread out like a pinned butterfly, muzzled and gagged so she couldn't twist anymore of their men's minds in order to escape. 

She was magnificent. An anomaly.  _ An asset. _

The perfect leverage and the final piece they needed to propel the twins to greatness. Very little else worked; but their singular successes were  _ magnificent _ . 

After all. There was nothing more horrifying than a miracle. 

 

**Author's Note:**

> This is a timeline change, where parts of Civil War happen before Age of Ultron. It's also more like a written post-credit scene, it's important to the course of the series, especially with some changes from canon that have occurred earlier on. 
> 
> Otherwise; I own nothing but my words and Sy! The Avengers and Percy Jackson worlds belong to their various creators. 
> 
> I love comments! Please always let me know what you think!


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